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diff --git a/dom/bindings/BindingDeclarations.h b/dom/bindings/BindingDeclarations.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A header for declaring various things that binding implementation headers
+ * might need.  The idea is to make binding implementation headers safe to
+ * include anywhere without running into include hell like we do with
+ * BindingUtils.h
+ */
+#ifndef mozilla_dom_BindingDeclarations_h__
+#define mozilla_dom_BindingDeclarations_h__
+
+#include "js/RootingAPI.h"
+#include "js/Value.h"
+
+#include "mozilla/Maybe.h"
+#include "mozilla/RootedOwningNonNull.h"
+#include "mozilla/RootedRefPtr.h"
+
+#include "mozilla/dom/DOMString.h"
+
+#include "nsCOMPtr.h"
+#include "nsStringGlue.h"
+#include "nsTArray.h"
+
+class nsIPrincipal;
+class nsWrapperCache;
+
+namespace mozilla {
+namespace dom {
+
+// Struct that serves as a base class for all dictionaries.  Particularly useful
+// so we can use IsBaseOf to detect dictionary template arguments.
+struct DictionaryBase
+{
+protected:
+  bool ParseJSON(JSContext* aCx, const nsAString& aJSON,
+                 JS::MutableHandle<JS::Value> aVal);
+
+  bool StringifyToJSON(JSContext* aCx,
+                       JS::Handle<JSObject*> aObj,
+                       nsAString& aJSON) const;
+
+  // Struct used as a way to force a dictionary constructor to not init the
+  // dictionary (via constructing from a pointer to this class).  We're putting
+  // it here so that all the dictionaries will have access to it, but outside
+  // code will not.
+  struct FastDictionaryInitializer {
+  };
+
+  bool mIsAnyMemberPresent = false;
+
+private:
+  // aString is expected to actually be an nsAString*.  Should only be
+  // called from StringifyToJSON.
+  static bool AppendJSONToString(const char16_t* aJSONData,
+                                 uint32_t aDataLength, void* aString);
+
+public:
+  bool IsAnyMemberPresent() const
+  {
+    return mIsAnyMemberPresent;
+  }
+};
+
+// Struct that serves as a base class for all typed arrays and array buffers and
+// array buffer views.  Particularly useful so we can use IsBaseOf to detect
+// typed array/buffer/view template arguments.
+struct AllTypedArraysBase {
+};
+
+// Struct that serves as a base class for all owning unions.
+// Particularly useful so we can use IsBaseOf to detect owning union
+// template arguments.
+struct AllOwningUnionBase {
+};
+
+
+struct EnumEntry {
+  const char* value;
+  size_t length;
+};
+
+class MOZ_STACK_CLASS GlobalObject
+{
+public:
+  GlobalObject(JSContext* aCx, JSObject* aObject);
+
+  JSObject* Get() const
+  {
+    return mGlobalJSObject;
+  }
+
+  nsISupports* GetAsSupports() const;
+
+  // The context that this returns is not guaranteed to be in the compartment of
+  // the object returned from Get(), in fact it's generally in the caller's
+  // compartment.
+  JSContext* Context() const
+  {
+    return mCx;
+  }
+
+  bool Failed() const
+  {
+    return !Get();
+  }
+
+  // It returns the subjectPrincipal if called on the main-thread, otherwise
+  // a nullptr is returned.
+  nsIPrincipal* GetSubjectPrincipal() const;
+
+protected:
+  JS::Rooted<JSObject*> mGlobalJSObject;
+  JSContext* mCx;
+  mutable nsISupports* MOZ_UNSAFE_REF("Valid because GlobalObject is a stack "
+                                      "class, and mGlobalObject points to the "
+                                      "global, so it won't be destroyed as long "
+                                      "as GlobalObject lives on the stack") mGlobalObject;
+};
+
+// Class for representing optional arguments.
+template<typename T, typename InternalType>
+class Optional_base
+{
+public:
+  Optional_base()
+  {}
+
+  explicit Optional_base(const T& aValue)
+  {
+    mImpl.emplace(aValue);
+  }
+
+  bool operator==(const Optional_base<T, InternalType>& aOther) const
+  {
+    return mImpl == aOther.mImpl;
+  }
+
+  template<typename T1, typename T2>
+  explicit Optional_base(const T1& aValue1, const T2& aValue2)
+  {
+    mImpl.emplace(aValue1, aValue2);
+  }
+
+  bool WasPassed() const
+  {
+    return mImpl.isSome();
+  }
+
+  // Return InternalType here so we can work with it usefully.
+  template<typename... Args>
+  InternalType& Construct(Args&&... aArgs)
+  {
+    mImpl.emplace(Forward<Args>(aArgs)...);
+    return *mImpl;
+  }
+
+  void Reset()
+  {
+    mImpl.reset();
+  }
+
+  const T& Value() const
+  {
+    return *mImpl;
+  }
+
+  // Return InternalType here so we can work with it usefully.
+  InternalType& Value()
+  {
+    return *mImpl;
+  }
+
+  // And an explicit way to get the InternalType even if we're const.
+  const InternalType& InternalValue() const
+  {
+    return *mImpl;
+  }
+
+  // If we ever decide to add conversion operators for optional arrays
+  // like the ones Nullable has, we'll need to ensure that Maybe<> has
+  // the boolean before the actual data.
+
+private:
+  // Forbid copy-construction and assignment
+  Optional_base(const Optional_base& other) = delete;
+  const Optional_base &operator=(const Optional_base &other) = delete;
+
+protected:
+  Maybe<InternalType> mImpl;
+};
+
+template<typename T>
+class Optional : public Optional_base<T, T>
+{
+public:
+  Optional() :
+    Optional_base<T, T>()
+  {}
+
+  explicit Optional(const T& aValue) :
+    Optional_base<T, T>(aValue)
+  {}
+};
+
+template<typename T>
+class Optional<JS::Handle<T> > :
+  public Optional_base<JS::Handle<T>, JS::Rooted<T> >
+{
+public:
+  Optional() :
+    Optional_base<JS::Handle<T>, JS::Rooted<T> >()
+  {}
+
+  explicit Optional(JSContext* cx) :
+    Optional_base<JS::Handle<T>, JS::Rooted<T> >()
+  {
+    this->Construct(cx);
+  }
+
+  Optional(JSContext* cx, const T& aValue) :
+    Optional_base<JS::Handle<T>, JS::Rooted<T> >(cx, aValue)
+  {}
+
+  // Override the const Value() to return the right thing so we're not
+  // returning references to temporaries.
+  JS::Handle<T> Value() const
+  {
+    return *this->mImpl;
+  }
+
+  // And we have to override the non-const one too, since we're
+  // shadowing the one on the superclass.
+  JS::Rooted<T>& Value()
+  {
+    return *this->mImpl;
+  }
+};
+
+// A specialization of Optional for JSObject* to make sure that when someone
+// calls Construct() on it we will pre-initialized the JSObject* to nullptr so
+// it can be traced safely.
+template<>
+class Optional<JSObject*> : public Optional_base<JSObject*, JSObject*>
+{
+public:
+  Optional() :
+    Optional_base<JSObject*, JSObject*>()
+  {}
+
+  explicit Optional(JSObject* aValue) :
+    Optional_base<JSObject*, JSObject*>(aValue)
+  {}
+
+  // Don't allow us to have an uninitialized JSObject*
+  JSObject*& Construct()
+  {
+    // The Android compiler sucks and thinks we're trying to construct
+    // a JSObject* from an int if we don't cast here.  :(
+    return Optional_base<JSObject*, JSObject*>::Construct(
+      static_cast<JSObject*>(nullptr));
+  }
+
+  template <class T1>
+  JSObject*& Construct(const T1& t1)
+  {
+    return Optional_base<JSObject*, JSObject*>::Construct(t1);
+  }
+};
+
+// A specialization of Optional for JS::Value to make sure no one ever uses it.
+template<>
+class Optional<JS::Value>
+{
+private:
+  Optional() = delete;
+
+  explicit Optional(const JS::Value& aValue) = delete;
+};
+
+// A specialization of Optional for NonNull that lets us get a T& from Value()
+template<typename U> class NonNull;
+template<typename T>
+class Optional<NonNull<T> > : public Optional_base<T, NonNull<T> >
+{
+public:
+  // We want our Value to actually return a non-const reference, even
+  // if we're const.  At least for things that are normally pointer
+  // types...
+  T& Value() const
+  {
+    return *this->mImpl->get();
+  }
+
+  // And we have to override the non-const one too, since we're
+  // shadowing the one on the superclass.
+  NonNull<T>& Value()
+  {
+    return *this->mImpl;
+  }
+};
+
+// A specialization of Optional for OwningNonNull that lets us get a
+// T& from Value()
+template<typename T>
+class Optional<OwningNonNull<T> > : public Optional_base<T, OwningNonNull<T> >
+{
+public:
+  // We want our Value to actually return a non-const reference, even
+  // if we're const.  At least for things that are normally pointer
+  // types...
+  T& Value() const
+  {
+    return *this->mImpl->get();
+  }
+
+  // And we have to override the non-const one too, since we're
+  // shadowing the one on the superclass.
+  OwningNonNull<T>& Value()
+  {
+    return *this->mImpl;
+  }
+};
+
+// Specialization for strings.
+// XXXbz we can't pull in FakeString here, because it depends on internal
+// strings.  So we just have to forward-declare it and reimplement its
+// ToAStringPtr.
+
+namespace binding_detail {
+struct FakeString;
+} // namespace binding_detail
+
+template<>
+class Optional<nsAString>
+{
+public:
+  Optional() : mPassed(false) {}
+
+  bool WasPassed() const
+  {
+    return mPassed;
+  }
+
+  void operator=(const nsAString* str)
+  {
+    MOZ_ASSERT(str);
+    mStr = str;
+    mPassed = true;
+  }
+
+  // If this code ever goes away, remove the comment pointing to it in the
+  // FakeString class in BindingUtils.h.
+  void operator=(const binding_detail::FakeString* str)
+  {
+    MOZ_ASSERT(str);
+    mStr = reinterpret_cast<const nsString*>(str);
+    mPassed = true;
+  }
+
+  const nsAString& Value() const
+  {
+    MOZ_ASSERT(WasPassed());
+    return *mStr;
+  }
+
+private:
+  // Forbid copy-construction and assignment
+  Optional(const Optional& other) = delete;
+  const Optional &operator=(const Optional &other) = delete;
+
+  bool mPassed;
+  const nsAString* mStr;
+};
+
+template<class T>
+class NonNull
+{
+public:
+  NonNull()
+#ifdef DEBUG
+    : inited(false)
+#endif
+  {}
+
+  // This is no worse than get() in terms of const handling.
+  operator T&() const {
+    MOZ_ASSERT(inited);
+    MOZ_ASSERT(ptr, "NonNull<T> was set to null");
+    return *ptr;
+  }
+
+  operator T*() const {
+    MOZ_ASSERT(inited);
+    MOZ_ASSERT(ptr, "NonNull<T> was set to null");
+    return ptr;
+  }
+
+  void operator=(T* t) {
+    ptr = t;
+    MOZ_ASSERT(ptr);
+#ifdef DEBUG
+    inited = true;
+#endif
+  }
+
+  template<typename U>
+  void operator=(U* t) {
+    ptr = t->ToAStringPtr();
+    MOZ_ASSERT(ptr);
+#ifdef DEBUG
+    inited = true;
+#endif
+  }
+
+  T** Slot() {
+#ifdef DEBUG
+    inited = true;
+#endif
+    return &ptr;
+  }
+
+  T* Ptr() {
+    MOZ_ASSERT(inited);
+    MOZ_ASSERT(ptr, "NonNull<T> was set to null");
+    return ptr;
+  }
+
+  // Make us work with smart-ptr helpers that expect a get()
+  T* get() const {
+    MOZ_ASSERT(inited);
+    MOZ_ASSERT(ptr);
+    return ptr;
+  }
+
+protected:
+  T* ptr;
+#ifdef DEBUG
+  bool inited;
+#endif
+};
+
+// Class for representing sequences in arguments.  We use a non-auto array
+// because that allows us to use sequences of sequences and the like.  This
+// needs to be fallible because web content controls the length of the array,
+// and can easily try to create very large lengths.
+template<typename T>
+class Sequence : public FallibleTArray<T>
+{
+public:
+  Sequence() : FallibleTArray<T>()
+  {}
+};
+
+inline nsWrapperCache*
+GetWrapperCache(nsWrapperCache* cache)
+{
+  return cache;
+}
+
+inline nsWrapperCache*
+GetWrapperCache(void* p)
+{
+  return nullptr;
+}
+
+// Helper template for smart pointers to resolve ambiguity between
+// GetWrappeCache(void*) and GetWrapperCache(const ParentObject&).
+template <template <typename> class SmartPtr, typename T>
+inline nsWrapperCache*
+GetWrapperCache(const SmartPtr<T>& aObject)
+{
+  return GetWrapperCache(aObject.get());
+}
+
+struct MOZ_STACK_CLASS ParentObject {
+  template<class T>
+  MOZ_IMPLICIT ParentObject(T* aObject) :
+    mObject(aObject),
+    mWrapperCache(GetWrapperCache(aObject)),
+    mUseXBLScope(false)
+  {}
+
+  template<class T, template<typename> class SmartPtr>
+  MOZ_IMPLICIT ParentObject(const SmartPtr<T>& aObject) :
+    mObject(aObject.get()),
+    mWrapperCache(GetWrapperCache(aObject.get())),
+    mUseXBLScope(false)
+  {}
+
+  ParentObject(nsISupports* aObject, nsWrapperCache* aCache) :
+    mObject(aObject),
+    mWrapperCache(aCache),
+    mUseXBLScope(false)
+  {}
+
+  // We don't want to make this an nsCOMPtr because of performance reasons, but
+  // it's safe because ParentObject is a stack class.
+  nsISupports* const MOZ_NON_OWNING_REF mObject;
+  nsWrapperCache* const mWrapperCache;
+  bool mUseXBLScope;
+};
+
+namespace binding_detail {
+
+// Class for simple sequence arguments, only used internally by codegen.
+template<typename T>
+class AutoSequence : public AutoTArray<T, 16>
+{
+public:
+  AutoSequence() : AutoTArray<T, 16>()
+  {}
+
+  // Allow converting to const sequences as needed
+  operator const Sequence<T>&() const {
+    return *reinterpret_cast<const Sequence<T>*>(this);
+  }
+};
+
+} // namespace binding_detail
+
+// Enum to represent a system or non-system caller type.
+enum class CallerType : uint32_t {
+  System,
+  NonSystem
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_BindingDeclarations_h__